Prior art references, such as U.S. Pat. No. 4,936,828 (Chiang, Kophu), U.S. Pat. No. 5,588,963 (Roelofs; Bernardus J. G. M.), and U.S. Pat. No. 6,213,354 (Kay, Robert L.) teach respective infusion systems which use optical systems to measure the volume of falling drops. That is, the principle of operation set forth in the prior art, and in the preceding references in particular, is necessarily connected to operations upon a drop that is in free fall through a drip chamber.